The exterior of a building shields the interior from outside environmental agents, from wind, rain and uncomfortable temperatures. A building's exterior may comprise a window that is set within a masonry or steel structure, or a solid wall of windows as in many modern skyscraper buildings. It may instead consist of a "curtain wall" of stone or metal slabs, or it may be any combination of these elements. Typically, these surface components are attached to the exterior of the building with a sill or "sill can", along with other perimeter support fixtures. FIGS. 1 and 2 illustrate a common arrangement. The sill 1, usually but not necessarily a trough extruded out of light weight aluminum, holds the window or curtain wall assembly 2 in place, seating it against the inner structure of the building 7.
The sill 1 possesses a distribution of holes or perforations (center hole 3 and elongated holes 4) through which bolts 5 and nuts 6 fasten the sill and window/curtain wall assembly 2 to the structure of the building 7. Depending on the weight, dimensions and materials used for the exterior building elements, other similar fasteners such as screws or concrete expansion anchors will be used to secure the elements against the building. Many of the holes in a window or curtain wall sill are elongated to allow for normal expansion and contraction of the metal sill and its corresponding exterior section. The fasteners within these elongated holes may freely move forward and backward along the holes, letting the sill and window (or wall) "breathe" with the thermal expansions and contractions of day/night cycles and seasonal changes. The building must also respond elastically to the torsional effects of wind, seismic tremors and normal settling. If sills did not allow such expansion, the exterior building elements would experience enormous undesirable buckling forces, tending to shatter windows and deform walls. Further, the constant strains of repeated expansions could loosen and undo all the support bolts, allowing entire sections of building walls to fall out.
Including such elongated expansion holes into the sills, however, tends to defeat the original purpose of a building exterior: no longer does the sill and window/wall combination hermetically seal the interior from the exterior. Water which collects naturally in the troughs of the sills may slowly leak through the sill holes, damaging the interiors of buildings and possibly weakening their support structures. At a minimum, expensive interior furnishings and wall treatments could be ruined. Even more serious, though, is the possibility of shorting out electrical systems, raising the chance of fires. Further, concrete and steel structures remain sensitive to the erosive effects of water damage: by damaging these support members, long term leakage can render a building completely unsafe and unusable.
Current building practice often makes two efforts at preventing leakage of water into a building and at leading the collected water away from the building interior. The first approach places weep holes 8, by drilling or some other appropriate method, at regular intervals in the exterior portion of each sill to allow trapped water to drain to the exterior of the building. But even with weep holes, a certain amount of water may remain in the sill due to exterior, positive wind pressure. And since in any case drainage takes time, the pool of draining water still has an opportunity to leak through the sill's fastener holes into the building.
Builders attempt to further prevent accumulated water from entering the building by applying some form of a sealant 9, typically a type of silicone adhesive, around the fasteners and holes in each sill can. By physically filling up these gaps in the sill, builders hope to completely prevent leakage. But again, the sill's elongated holes exist to allow normal expansion and contraction of the exterior. Hence, the silicone seals suffer shearing forces from the thermal movement of the window/sill assembly and must be able to take the compressions and extensions repeatedly over a long period of time. But, like most elastically stressed elements, many silicone seals simply cannot perform faithfully forever. They may eventually work loose or rupture, allowing water once again to leak into a building, often weeks or years after construction has finished.
In addition, if the silicone and other plastic seals physically contact the fastener, whether screw, bolt or concrete anchor, the metals and chemicals of the fastener may attack the sealant material. By allowing oxidation and chemical degradation of the sealant, this contact between fastener and sealant can, independent of any thermal stresses, cause failure of the seals and lead to damage of building interiors and structures. Hence, any perforation of a building's exterior, where fixtures such as lighting elements, chimney flues, advertising displays, etc. are attached with fasteners that are then sealed over, remains vulnerable to sealant failure and consequent interior damage.
The building construction industry has faced a great challenge to find ways to seal and protect the interiors of offices and homes from the exterior, harsh elements. A method of sealing building perforations against water leakage and other environmental agents, which withstands harmful expansions and contractions and also chemical degradations, would represent a major technological advance. The ability to cheaply and reliably seal a building's exterior would satisfy a long-felt need within the industry and offer to the contracting industry a versatile, faithful and inexpensive sealing method and device.